Arbitrary Pressures Research Articles

Data-driven design of high pressure hydride superconductors using DFT and deep learning

The observation of superconductivity in hydride-based materials under ultrahigh pressures (for example, H3S and LaH10) has fueled the interest in a more data-driven approach to discovering new high-pressure hydride superconductors. In this work, we performed density functional theory (DFT) calculations to predict the critical temperature ( Tc ) of over 900 hydride materials under a pressure range of (0–500) GPa, where we found 122 dynamically stable structures with a Tc above MgB2 (39 K). To accelerate screening, we trained a graph neural network (GNN) model to predict Tc and demonstrated that a universal machine learned force-field can be used to relax hydride structures under arbitrary pressures, with significantly reduced cost. By combining DFT and GNNs, we can establish a more complete map of hydrides under pressure.

A Practical Approach for Ischemic Preconditioning Intervention in Sports: A Pilot Study for Cuff Thigh Occlusion Pressure Estimation Based on Systolic Blood Pressure.

For the ischemic preconditioning (IPC) intervention, the accuracy of the protocol is paramount for mediating its possible ergogenic effects. However, the lack of standardization and widespread use of arbitrary cuff pressures (ranging from 130 to >300 mmHg) have been predominantly observed, potentially affecting the results and compromising the reproducibility of findings. Thus, the purpose of this study was to determine an appropriate cuff pressure during IPC. Seventeen healthy male participants were enrolled in the study. Anthropometric measurements were initially conducted, followed by systolic and diastolic blood pressure measurements. Subsequently, we determined the individual thigh occlusion pressure (TOP) for the right leg using a hand-held Doppler device. Based on these findings, we developed an estimation equation for TOP, considering the current brachial systolic blood pressure (SBP) values. We then conducted a retrospective analysis of its capacity to mediate occlusion. We observed the ability to estimate TOP using the equation (p = 0.01; ES: 0.86), presenting ~6% superiority in absolute values for occlusion compared to direct measurement (TOP equation: 169.9 ± 9.1; TOP direct measured: 161.2 ± 11.1). However, TOP estimation was insufficient to produce complete occlusion in two out of 17 subjects (11.8%). In conclusion, the estimation of TOP incorporating SBP values may offer a valid and practical means for cuff administration during IPC protocols with potential to minimize adverse effects and maximize its positive effects.

Biomimetic Electronic Skin for Robots Aiming at Superior Dynamic-Static Perception and Material Cognition Based on Triboelectric-Piezoresistive Effects.

Empowering robots with tactile perception and even thinking as well as judgment capabilities similar to those of humans is an inevitable path for the development of future robots. Here, we propose a biomimetic electronic skin (BES) that truly serves and applies to robots to achieve superior dynamic-static perception and material cognition functionalities. First, the microstructured triboelectric and piezoresistive layers are fabricated by a facile template method followed by selected self-polymerization treatment, enabling BES with high sensitivity and a wide detection range. Further, through laminated-independent triboelectric and piezoresistive parts for perceiving dynamic and static pressures simultaneously, the BES is capable of supporting the robot hand to monitor the entire process during object grasping. Most importantly, by further combining a neural network model, an intelligent cognition system is constructed for real-time cognition of the object material species via one touch of the robot hand under arbitrary pressures, which goes beyond the human cognition ability.

Моделювання вимушених гармонічних коливань прямокутного фундамента на водонасиченій шаруватій основі

A numerical study of the dynamic contact problem is carried out by the method of orthogonal polynomials. А symbolic solution was found for the double transformants of the vertical displacements of the layered two-phase poroelastic liquid saturated base under the action of arbitrary vertical contact pressures. Numerical analysis was performed for the Rayleigh function and the components of displacements in the kernels of integrable functions. An example of calculating double integrals necessary to determine the contact pressures of two-phase soil under the base of the foundation is given.

Analytical stress and displacement of twin noncircular tunnels in elastic semi-infinite ground

In general, twin noncircular tunnels may cause high stress concentrations and large settlements because of the strong interaction between tunnels and their noncircular shape. In this study, new analytical solutions are presented to efficiently predict the elastic stresses and displacements around shallow twin noncircular tunnels in rocks. The key factors, i.e., the real interactions between tunnels, arbitrary tunnel shapes, arrangements and pressures exerted at the internal tunnel boundaries due to liners or water pressures, are fully taken into account.The Schwartz alternating method is used to reduce the twin noncircular tunnels problem to a series of problems where only one noncircular tunnel is contained in the half-plane. Then, the solutions to the problem of a noncircular tunnel in the half-plane are obtained by complex variable theory combined with conformal mapping. Finally, convergent and highly accurate analytical solutions of twin noncircular tunnels are achieved by superposing the solutions of the reduced single tunnel problems. The analytical solutions are verified by the good agreement between the analytical and FEM results under the same assumptions. The proposed analytical solution can help to reveal the mechanical mechanisms of ground responses due to twin tunnelling in an elastic semi-infinite ground.

Hyperelastic Modeling and Validation of Hybrid-Actuated Soft Robot with Pressure-Stiffening.

Soft robots have gained popularity, especially in intraluminal applications, because their soft bodies make them safer for surgical interventions than flexures with rigid backbones. This study investigates a pressure-regulating stiffness tendon-driven soft robot and provides a continuum mechanics model for it towards using that in adaptive stiffness applications. To this end, first, a central single-chamber pneumatic and tri-tendon-driven soft robot was designed and fabricated. Afterward, the classic Cosserat's rod model was adopted and augmented with the hyperelastic material model. The model was then formulated as a boundary-value problem and was solved using the shooting method. To identify the pressure-stiffening effect, a parameter-identification problem was formulated to identify the relationship between the flexural rigidity of the soft robot and internal pressure. The flexural rigidity of the robot at various pressures was optimized to match theoretical deformation and experiments. The theoretical findings of arbitrary pressures were then compared with the experiment for validation. The internal chamber pressure was in the range of 0 to 40 kPa and the tendon tensions were in the range of 0 to 3 N. The theoretical and experimental findings were in fair agreement for tip displacement with a maximum error of 6.40% of the flexure's length.

Study on the Influence of Internal Water Pressure on the Internal Force of Circular Hydraulic Tunnel Lining

The internal water pressure condition influences the internal force of the circular hydraulic tunnel lining. However, calculating the lining’s internal force of this type of tunnel still lacks practical theory. Based on the modified routine method and the theory of structural mechanics, the internal stress model of the tunnel section is established in this paper. The general calculation formula of lining internal force is deduced by considering arbitrary water level height and different water conveyance pressures. The formula is used to calculate the internal force of the lining under the action of internal water pressure and the influence laws of water level height and water conveyance pressure are explored, respectively. In addition, case analysis was carried out for several typical projects. The results show that the maximum internal force of the lining increases with the increase of water pressure and inner radius and the maximum internal force is in a fixed special position when the water is conveyed under pressure. When the water is conveyed without pressure, the internal force of the lining will increase with the increased water level. However, the maximum bending moment and axial force will reduce at the special water level. This calculation theory considering different working conditions of internal water pressure solves the calculation problem of the internal force of a circular hydraulic tunnel. It improves the design theory of tunnel structure and provides a theoretical basis for this type of tunnel’s structural design and safe operation.

High pointwise emergence and Katok’s conjecture for symbolic systems with non-uniform structure

Recently, Kiriki, Nakano and Soma introduced a concept called pointwise emergence as a new quantitative perspective into the study of non-existence of averages for dynamical systems. In the present paper, we consider the set of points with high pointwise emergence for symbolic systems with non-uniform structure and prove that this set carries full topological pressure. For the proof of this result, we show that such systems have ergodic measures of arbitrary intermediate pressures.

Isobaric Expansion Engine Compressors: Thermodynamic Analysis of the Simplest Direct Vapor-Driven Compressors

Isobaric expansion (IE) technology is a promising solution for mini- and medium-scale low-grade heat utilization. IE engines directly convert heat to mechanical energy and are particularly interesting as direct-acting, vapor-driven pumps and compressors. The elimination of multiple energy transformations, technical simplicity and the ability to use widely available low-grade heat (<100 °C) instead of fossil fuels are attractive features of this technology. The purpose of this paper was to present a new compression technology based on IE Worthington type engines, analyze the process analytically and numerically, and provide a first assessment of its potential. The simplest single- and double-acting schemes were considered for arbitrary low and high pressures of the compressed gas/vapor and driving vapor. In these schemes, the compressor piston was rigidly connected to that of an engine/driver. The vapor use efficiency of the driver process was characterized by the ratio of the network carried out in the cycle to the consumed mass of the driving vapor. The performed thermodynamic analysis showed how the vapor use efficiency depends on the process parameters. It was found that the efficiency of vapor use in the simplest schemes was low in comparison with the efficiency in pumps if the compressor work was much less than the pump work at the same pressure ratio. This occurred because the energy of the driving vapor was spent on the compression of the vapor itself. As a result, the thermal efficiency of the IE engine compressors was lower than that of the IE engine pumps. The difference was very large if the work of the engine feed pump was significant and no heat regeneration is applied. The results obtained are very useful for achieving improvements in this interesting technology, which will be reported in subsequent publications.

Real gas effects in sound wave propagation through two-phase systems

We study sound wave propagation through a two-phase system of gas with dispersed liquid droplets. The key element of the study is a combination of real gas effects, entering the model via a suitable equation of state, with steady and unsteady contributions to the drag force and heat transfer. This feature makes the model applicable for arbitrary pressures and temperatures. In the cases of low and high wave frequencies, ω, analytical solution is derived. At low ω, the model yields a generalization of the homogenous flow approximation to real gases. At high ω, the speed of sound tends to its value in the real gas in the absence of droplets while the attenuation coefficient diverges as ω. The model predicts the phenomenon of resonant attenuation demonstrated by the maximum of the growth rate of attenuation coefficient when ω is close to the eigen frequency of particle relaxation. In the absence of droplets (single-phase limit) for the gas satisfying the van der Waals equation of state, the model yields the corresponding states principle for the speed of sound: The ratio of the actual speed of sound to its ideal-gas value is the universal function of reduced density and temperature. This ratio demonstrates a nonmonotonous behavior of the speed of sound as a function of density reflecting the competition between the repulsive and attractive terms in the intermolecular interaction potential.

Thermodynamics of spin crossover in ferropericlase: an improved LDA + Usc calculation

We present LDA + Usc calculations of high-spin (HS) and low-spin (LS) states in ferropericlase (fp) with an iron concentration of 18.75%. The Hubbard parameter U is determined self-consistently with structures optimized at arbitrary pressures. We confirm a strong dependence of U on the pressure and spin state. Static calculations confirm that the antiferromagnetic configuration is more stable than the ferromagnetic one in the HS state, consistent with low-temperature measurements. Phonon calculations guarantee the dynamical stability of HS and LS states throughout the pressure range of the Earth mantle. Compression curves for HS and LS states agree well with experiments. Using a non-ideal mixing model for the HS to LS states solid solution, we obtain a crossover starting at ∼45 GPa at room temperature and considerably broader than previous results. The spin-crossover phase diagram is calculated, including vibrational, magnetic, electronic, and non-ideal HS–LS entropic contributions. Our results suggest the mixed-spin state predominates in fp in most of the lower mantle.

Analytical solutions of noncircular tunnels in viscoelastic semi-infinite ground subjected to surcharge loadings

The construction of noncircular tunnels at shallow depths has become increasingly common in urban areas to efficiently utilize underground space. In general, noncircular tunnels may cause high stress concentrations and large settlements. In addition, the stability of shallow tunnels affected by the structural loads/surcharge loads on the surface is too significant to ignore. This study presents new analytical solutions to efficiently predict the stresses and displacements around shallow noncircular tunnels in rheological rock. The key factors, i.e., any viscoelastic characteristics of the surrounding rock, arbitrarily distributed loads exerted on the ground surface, arbitrary tunnel shapes and pressures exerted at the internal tunnel boundaries due to liners or water pressures, are fully taken into account. A noncircular tunnel in the half-plane was mapped into an anulus by employing the conformal mapping function. Then, the elastic solutions of the problem are obtained by complex variable theory combined with the mapping function. Based on the elastic solutions and the extended corresponding principle for the viscoelastic problem, time-dependent analytical solutions are obtained for the ground assuming any viscoelastic models. The analytical solutions are verified by the good agreement between the analytical and FEM results under the same assumptions. Then, a parametric study is finally performed to investigate the influence of the location or range of the surcharge, tunnel burial depth and lateral pressure coefficient on the ground stresses and displacements. The proposed analytical solution can provide insight into the mechanical behavior of shallow noncircular tunnels under surcharge loads, as well as an alternative method in the preliminary designs of future shallow tunnels.

Wafer-level fabrication of alkali vapor cells using in-situ atomic deposition

We demonstrate a new technique for filling mm-scale microfabricated silicon and glass cavities with alkali vapors at the wafer-scale. A single etched silicon wafer contains an array of cavities containing alkali precursor materials offset laterally from the cell array. The wafer is heated to create an array of alkali droplets on an upper glass wafer, which is then translated laterally under vacuum and bonded to create the cells. This technique can be implemented in a commercially available bonding tool, allows the fabrication of cells with arbitrary buffer gas contents and pressures and can potentially produce cells with dimensions below 100 µm.

Approaches to determining occlusion pressure for blood flow restricted exercise training: Systematic review

ABSTRACT Low-intensity exercise with blood flow restriction (BFR) is an increasingly common method of improving muscular strength and hypertrophy, and improving aerobic fitness, in clinical and athletic populations. The aim of this systematic review was to describe common approaches to determining occlusion pressures for BFR exercise. A comprehensive literature search yielded 1389 results, of which 129 were included. Studies were predominantly randomised control trials (86.7%) with modest sample sizes (average number of 11.4 ± 6.2 participants per BFR group/s) of young adults (average age of 34.6 ± 17.9). Five different approaches for determining occlusion pressure were identified: arbitrary pressures (56.6%), percentage of limb occlusion pressure (25.6%), brachial systolic blood pressure (10.9%), perceived tightness (3.9%) and other (3%). From 2016 to 2018, the number of published papers using a percentage of limb occlusion pressure increased yearly, paralleling a decrease use of arbitrary pressures. Of the studies included in this review, the most common approach to determining occlusion pressure was using a non-individualised, arbitrary pressure. Given the safety concerns associated with arbitrary pressures, continual dissemination regarding the optimal applications of BFR for safety and efficacy is required.

Analytical solution of displacement and stress induced by the sequential excavation of noncircular tunnels in viscoelastic rock

The sequential excavation of a tunnel cross-section is usually employed in large scale tunnel construction to reduce the excavation impact on surrounding rock. Time-dependent sequential excavation combined with rock rheology makes the mechanical response of the surrounding rock a complex function of time, and it is possibly closely related to the excavation path. This study presents new analytical solutions that account for an arbitrary sequential excavation of the tunnel's cross-sections, the ground's viscoelastic properties, arbitrary tunnel shapes and pressures exerted at the internal tunnel boundaries due to liners or water pressures. The time-dependent analytical solutions for the stresses and displacements in each excavation step are derived by complex variable theory, conformal mapping and the Laplace transform technique. The solutions agree very well with the FEM numerical results for models that are completely consistent, and they are qualitatively consistent with the field data. In addition, the mechanical mechanism of the time-dependency of the displacement is analyzed in detail for two types of viscoelastic models. Then parametric analyses are conducted for the sequential excavation of a rectangular tunnel, a semi-arched tunnel with a vertical wall and a horseshoe tunnel to investigate the influence of the excavation sequences, excavation time and the supporting pressures on the ground displacements and stresses. The proposed analytical solutions can help reveal the particular mechanical mechanism of the time-dependent ground responses due to sequential excavations combined with rock rheology, as well as provide an alternative method in the preliminary designs of future tunnels.

LDA+Usc calculations of phase relations in FeO

Using the LDA+$\textit{U}_\text{sc}$ method, we present calculations phase relations of iron monoxides involving five polytypes in multiple spin-state configurations. The Hubbard parameter $U$ is determined self-consistently simultaneously with the occupation matrix and structures at arbitrary pressures. The Hubbard parameter strongly depends on pressure, structure, and spin state. Comparison with experimental structural data indicates the LDA+$\textit{U}_\text{sc}$ can predict structure, compression curves, phase relations, and transition pressures very well for the insulating B1 and iB8 states. However, it requires additional calculations using the Mermin functional that includes the electronic entropic contribution to the free energy to obtain an nB8 metallic state and a consistent iB8 to nB8 insulator-to-metal transition pressure.

Physical understanding of keyhole and weld pool dynamics in laser welding under different water pressures

Underwater laser welding, an efficient and labor-saving in-situ repair technology, is prospective in the field of underwater environment manufacturing. It simplifies the tedious process of disassembly and transportation when the underwater facilities are usually repaired ashore. However, the keyhole and weld pool dynamics in laser welding under different water pressure are little understood. In this study, we developed a mathematical model of underwater laser welding process with arbitrary ambient pressures for the first time. The underlying physics of the underwater laser welding process was explored, and the keyhole and weld pool dynamics between the underwater environment and the ground were compared. Results showed that a keyhole similar to that in the atmosphere is also formed in the water environment. And the keyhole was oscillated. The surface of the weld pool in contact with water cooled quickly, forming a special morphology of the weld pool. The flow in the weld pool was mainly driven by the recoil pressure. The temperature of the surface of the keyhole increased with the increase of water depth. That is because the laser beam energy density is large enough to heat the local metal to the boiling point which increases with the ambient pressure increase. It means that the weld pool was able to absorb more energy before evaporation. Then, less energy is applied to induce the recoil pressure to deepen the keyhole. As a result, a shallower but more stable keyhole is formed in underwater laser welding process under 5 MPa pressure. This study can provide better understanding of the heat and mass transfer behaviors in underwater laser welding.

Evolutionary optimization of PAW data-sets for accurate high pressure simulations

We examine the challenge of performing accurate electronic structure calculations at high pressures by comparing the results of all-electron full potential linearized augmented-plane-wave calculations, as implemented in the WIEN2k code, with those of the projector augmented wave (PAW) method, as implemented in Quantum ESPRESSO or Abinit code. In particular, we focus on developing an automated and consistent way of generating transferable PAW data-sets that can closely produce the all electron equation of state defined from zero to arbitrary high pressures. The technique we propose is an evolutionary search procedure that exploits the ATOMPAW code to generate atomic data-sets and the Quantum ESPRESSO software suite for total energy calculations. We demonstrate different aspects of its workability by optimizing PAW basis functions of some elements relatively abundant in planetary interiors. In addition, we introduce a new measure of atomic data-set goodness by considering their performance uniformity over an extended pressure range.

Computational methodology for solubility prediction: Application to the sparingly soluble solutes.

The solubility of a crystalline substance in the solution can be estimated from its absolute solid free energy and excess solvation free energy. Here, we present a numerical method, which enables convenient solubility estimation of general molecular crystals at arbitrary thermodynamic conditions where solid and solution can coexist. The methodology is based on standard alchemical free energy methods, such as thermodynamic integration and free energy perturbation, and consists of two parts: (1) systematic extension of the Einstein crystal method to calculate the absolute solid free energies of molecular crystals at arbitrary temperatures and pressures and (2) a flexible cavity method that can yield accurate estimates of the excess solvation free energies. As an illustration, via classical Molecular Dynamic simulations, we show that our approach can predict the solubility of OPLS-AA-based (Optimized Potentials for Liquid Simulations All Atomic) naphthalene in SPC (Simple Point Charge) water in good agreement with experimental data at various temperatures and pressures. Because the procedure is simple and general and only makes use of readily available open-source software, the methodology should provide a powerful tool for universal solubility prediction.

The high‐pressure viscosity of refrigerant/oil systems

AbstractApplication of the new quantitative elastohydrodynamics to the concentrated contacts operating within refrigerant compressors will require the accurate description of the viscosity of the lubricant that is diluted by the refrigerant. This article presents extensive viscosity measurements on polyolester and polyvinylether oils and their mixtures with low mass fractions (2–23%) of refrigerants R134a and R410a. Pressures up to 400 MPa and temperatures to 100°C were reached. Correlations are presented to predict the viscosity and pressure–viscosity coefficients at arbitrary temperatures and pressures and concentrations. Pressure–viscosity coefficients are compared with those derived from film thickness measurements using one of the popular definitions for the coefficient. Where comparisons can be made, the film‐derived pressure–viscosity coefficients were mostly inaccurate. Part of the problem has been the lack of a single well‐accepted and rigorous definition of the pressure–viscosity coefficient and the lack of an accurate film thickness formula that employs that definition. Copyright © 2017 John Wiley & Sons, Ltd.